Physiological responses in Macadamia integrifolia on exposure to manganese treatment Academic Article uri icon


  • Macadamia integrifolia Maiden & Betche (Proteaceae) from eastern Australia is farmed for its edible nuts and is capable of accumulating high foliar concentrations of manganese (Mn). It was investigated here in a pot trial, where a range of physiological responses to Mn treatment were measured. Although Mn uptake was initially slow, final foliar concentrations increased linearly with treatment levels. The highest observed mean foliar concentration of Mn was 7900 μg g–1 dry weight (dwt). No negative effect of Mn accumulation on plant growth was apparent, even at the highest treatment concentration. Two groups of plants, each exposed to either full sunlight or part shade were identically treated with Mn. At the highest treatment concentration of Mn, the mean foliar concentrations of Mn of the former group were found to be significantly higher than those of the latter. Because M. integrifolia is cyanogenic, leaf cyanogenic glycosides were quantified to test for a relationship between the known chemical defence strategy of cyanogenesis and a proposed one of Mn accumulation. However, further studies are required to clarify this. Quantitative organic acid analyses showed that oxalate ion may bind excess Mn in M. integrifolia leaves. That Mn is not accumulated in M. integrifolia fruit could render the species potentially useful for remediating Mn-affected soils long-term, while serving as a food crop.

publication date

  • 2009